The present invention relates generally to fuel caps and particularly to a system for field testing the leakage level of fuel caps more particularly, the present invention relates to a portable fuel cap leakage tester for enabling a technician to determine if a fuel cap for providing a sealed closure on a vehicle fuel tank filler neck leaks at a rate that is equal to or less than a specified maximum acceptable fuel cap leak rate.
In-Use Maintenance (I/M) regulations enforced in many states require the inspection, diagnosis, and repair of a fuel system, liquid and vapor leaks as part of the yearly vehicle testing. More specifically, the testing requirement is included in the I/M240 regulation. Typically, to conduct these tests, testers have pressurized the system to be tested and timed the rate of pressure decay to determine passage or failure. This method has variable accuracy depending on the atmosphere pressure and other variables and can take considerable lengths of time if the leak is very small. An example of a prior art system which was capable of performing a system leakage test is described in U.S. Pat. No. 4,497,290 to Robert S. Harris and assigned to Stant Manufacturing Inc. Apparatus for automated testing of vehicle fuel caps is disclosed in U.S. Pat. No. 5,323,640 to Porcaro et al.
The simplest and most inexpensive portion of the system which can be replaced if it is the source of the leak is the fuel cap. The system test does not isolate the source of the leak and generally does not include the fuel cap since the tester is connected to the filler neck where the fuel cap is inserted. Thus, there exists a need for testing the fuel cap independent of the system to determine whether it meets the required standards and specifications.
According to the present invention, a first and a second passage having equal restrictions connected to an inlet which receives a source of pressurized fluid such as air is provided. A restriction is placed at the outlet of first passage and the cap to be tested is placed at the outlet of the second passage. The restriction at the outlet of the first passage is set to a desired leak rate standard. Because of these equal flow restrictions in the first and second passages, as the flow rate of air in one of those passages increases the pressure of air in that one passage decreases and thus the flow rate in a passage is inversely proportional to the pressure in that passage.
An indicator is connected to the first passage between the inlet and outlet restrictions and to the second passage between the inlet restriction and the outlet for indicating if the leakage at the outlet receiving the cap therein is greater or lesser than the flow rate of the restriction that is placed at the outlet of the first passage. If the cap to be tested leaks at an unacceptably high rate and thus fails the test, the indicator will show that the flow rate of pressurized air in the standardized first passage is lesser than the flow rate of pressurized air in the cap-receiving second passage. If the cap to be tested is characterized by zero leak or an acceptably low leak and thus passes the test, the indictor will show that the flow rate of pressurized air in the standardized first passage is greater than the flow rate of air in the cap-receiving second passage.
The indicator may be a U-shaped manometer having a leg connected to the first passage and another leg coupled one to the second passage. Alternatively, the indicator may be a pneumatic differential pressure gauge or an electrical differential pressure gauge. An inlet valve is provided to connect and disconnect the source of pressure to the first and second passages for initiating and terminating a test. If an electrical differential pressure gauge is used, a switch for activating and deactivating the pressure gauge is simultaneously operated with the operation of the valve for initiating and terminating the test. The indicator can quantitatively or qualitatively indicate the results of the test. The source of pressure includes a reservoir charged by a pump which may be a manually-operated or battery-operated pump.
In preferred embodiments, the fuel cap leakage tester is designed to be operated by a technician conducting an inspection to determine if the leakage of a designated test fuel cap is equal to or less than a specified leak rate and acceptable or if greater than the maximum specified, a failure which must be repaired or replaced. This specification describes a tester, which measures air pressure to detect actual leakage flow rate of the test cap and compares it to the flow rate of a designated master orifice on each test.
The tester is self-contained and capable of providing a positive pass-fail indication without any external input requirement. The tester provides a visual indications of test status with colored L.E.D. signals. Signals provided include READY-TO-TEST; PASS; FAIL; AND LOW BATTERY. The tester is designed to complete testing sequence to positive Pass/Fail indication in fifteen (15) seconds maximum duration after the technician signals cap installation by pressing a test button mounted on the tester.
The tester is portable and low-weight. A loop-type shoulder strap is provided for carrying the tester. All elements of the tester which affect calibration (i.e. Master Orifice) are concealed to minimize tampering. Cover plates and housings which allow access to tester operating components are attached with tamper-resistant fasteners requiring special tools (which are not readily available) for removal.
The tester is equipped with a hand-operated pump capable of pressurizing an air reservoir. The pump is equipped with one-way outlet check valve which retains pressure in the air reservoir to minimum test levels for a period of one (1) minute with the tester at rest after fully charging the air reservoir. The tester is provided with an overpressure regulator which controls maximum reservoir pressure to the specified level.
A Pass/Fail characteristic of each cap to be tested is determined by using the tester to make a flow comparison of the test cap to a master orifice which has a rated flow at a specified test pressure. The tester is provided with an operator-controlled test actuator switch which supplies test air from the air reservoir to a pneumatic circuit. The test actuator switch is normally off and requires the technician to activate switch for test duration.
The tester will detect reservoir pressure and flash a READY-TO-TEST indicator when air reservoir pressure is within test parameters. Pressure detectors on board the tester are activated automatically each time the tester is picked up by a technician in response to operation of a motion-activated on/off switch on board the tester. When the technician presses the test actuator switch button, the tester will monitor pneumatic circuit pressure and make a Pass/Fail leakage (flow) comparison when the Master Orifice is at the designated test pressure and flash either a FAIL or PASS indicator. The PASS or FAIL indicator shall remain on for ten (10) seconds. If a test is initiated, but pneumatic circuit pressure is not correct, the tester circuit will continue to monitor until eighteen (18) seconds has elapsed, then cycle both PASS and FAIL lights for two (2) seconds and then return to the Not Ready to Test state.
Additional objects, features, and advantages, of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.